The broad, long-term objective of this proposal is to utilize the genetically tractable model organism, S. cerevisiae, to study the cellular function of the Niemann-Pick disease type C (NP-C) protein, NPC1. NP-C is a fatal neurodegenerative disorder with a prevalence of 1 in 150,000 live births. Biochemically, NP-C is a lipid storage disorder marked by the lysosomal accumulation of unesterified cholesterol. The recent cloning of the NPC1 and NPC2/HEJ genes, which are causative in NP-C disease, established the molecular basis for NP-C, but the functions of the NPC proteins have yet to be determined. The specific aims of this proposal will test the feasibility of using S. cerevisiae as a model system to study NPC1 function. The specific aims are: 1) to test the hypothesis that the S. cerevisiae homolog of NPC 1, NCR 1, is required for retrograde transport from the vacuole; and 2) to determine whether S. cerevisiae can be used as a model system to assess the functional consequences of patient mutations in the NPC1 gene. We will utilize fluorescently labeled lipids to test whether yeast cells lacking the NCR1 protein are defective in retrograde transport from the vacuole. To examine the functional consequences of patient mutations in NPC1, we will take advantage of a growth phenotype we have identified in yeast that lack a functional NCR1/NPC1 protein to assay for functional complementation. The health relatedness of this project is the establishment of a basis and possible future diagnostic tool for Niemann Pick disease type C.